Containers that contain adsorbents to remove vaporous impurities in the atmosphere are well known. For example, they can be used to remove water vapor from air to obtain or maintain a dry atmosphere in applications where a moisture-free atmosphere is important, as for example in keeping hygroscopic materials dry. Another example is the removal of organic vapors from air to avoid contamination of local environments sensitive to such vapors, as for example in preventing head (stiction) failures in computer disk drives.
It is well known that greater effectiveness in removing of material from the atmosphere by adsorption can be obtained if the surface area of the adsorbent is maximized. Thus the smaller the adsorbent materials in particle size, the greater the effectiveness in removing impurities. Unfortunately, the smaller the particle size, the greater amount of dust-like fines that can be present. Moreover, even coarse adsorbent materials generate fines by mutual abrasion of the coarse granules.
To protect the adsorbent particles, a protective porous material i.e., a material that permits passage through it of gaseous components or other components is usually employed to surround and encase the adsorbent. But if the pores of the protective material are too large, the fines of the adsorbant material will escape through the pores and contaminate the outside environment. To prevent such escape, it is desirable for the protective covering to have pores small enough to prevent escape of very small diameter fines, i.e., fines on the order of 10 microns, or even 1 micron or less in size.